1. Field of the Invention
The present invention relates to an optical pickup device, an optical disc device and a prism, and is suitably applied to an optical disc device corresponding to e.g., CD (Compact Disc) and DVD (Digital Versatile Disc).
2. Background Art
An objective lens is formerly arranged in the downward direction of an optical disc mounted in a horizontal direction as an optical pickup in the optical disc device. A rising prism having a rising reflection angle θA set to 45° with respect to the horizontal direction of a rising reflection face is arranged further in the downward direction of this objective lens. A light beam emitted in the horizontal direction from a laser diode is deflected 90° by this rising prism. Thus, this light beam is irradiated to the optical disc through the objective lens.
In the optical pickup, thin formation is required as the optical disc device is made compact.
The above objective lens is moved in the vertical direction over a predetermined focus stroke range to retrieve a focusing point with respect to an information recording layer of the optical disc. Accordingly, in the vicinity of this objective lens, it is necessary to secure a space of this focus stroke range in addition to the thickness of the objective lens and the thickness of the rising prism arranged in the downward direction of the objective lens. The thickness of this objective lens vicinity determines the thickness of the entire optical pickup in many cases.
Therefore, there is a structure in which the optical pickup is thinly made by reducing the thickness of the rising prism by reducing the rising reflection angle θ in the rising prism (e.g., see JP-A-6-215413 (patent document 1)).
As shown in FIG. 7, the rising prism 4 in this optical pickup 1 refracts the light beam upward toward a reflection transmission face 4C by an incident face 4A, and reflects this refracted light beam downward toward a rising reflection face 4B by the reflection transmission face 4C. The rising prism 4 then reflects the reflected light beam in the upward direction toward the reflection transmission face 4C by the rising reflection face 4B. In the rising prism 4, an incident angle with respect to the reflection transmission face 4C of the light beam reflected on the rising reflection face 4B is a right angle equal to a critical angle or more. Therefore, this light beam is transmitted through the reflection transmission face 4C. As this result, the light beam is emitted in a direction perpendicular to the optical disc 100.
Thus, the rising prism 4 increases a descent angle of the light beam with respect to the horizontal direction at an incident time from the reflection transmission face 4C to the rising reflection face 4B, and can set a rising reflection angle θB to be less than 45°. Therefore, the thickness of the rising prism 4 can be reduced, and the optical pickup 1 can be thinly made in comparison with the former rising prism of rising reflection angle θA=45°.
Further, there is an optical pickup set to be made thinner near this objective lens (e.g., see Japanese Patent No. 3542065 (patent document 2)). As shown in FIG. 8, similar to the above rising prism 4, a rising prism 6 in this optical pickup 7 emits the light beam incident by following an incident face 6A, a reflection transmission face 6C, a rising reflection face 6B and a reflection transmission face 6C.
At this time, the optical pickup 7 rotates and arranges the rising reflection face 6B of the rising prism 6 in a lowering direction, and greatly inclines the reflection transmission face 6C from the horizontal direction. The optical pickup 7 then transmits the light beam reflected from the rising reflection face 6B in a low position portion of the reflection transmission face 6C. Thus, the light beam can be emitted from a position lower than the upper end of a light flux of the light beam at an incident time point. Further, the height of the vicinity of the objective lens can be reduced by storing one portion of the objective lens 5 to a space generated by the inclination. As a result, the optical pickup 7 can be thinly made.